(1) Field of the Invention
The present invention relates to a process for preparing a novel shaped article having a thick section composed of a polycyclic norbornene polymer. More particularly, the present invention relates to a process for preparing a shaped article of a thick section having no pores or voids in the interior, high mechanical strengths and a reduced water-absorbing property.
(2) Description of the Related Art
The technique of forming a processing stock such as a rod, a plate, a tube or a sheet from engineering plastics such as a polyimide resin, an aromatic polyamide resin, a polyacetal resin, super-high-molecular-weight polyethylene, polybutylene terephthalate or a polycarbonate resin, and subjecting the stock to machining such as cutting as in the case of a metal stock, is known.
The machining of plastic stock is superior to an injection molding thereof in various points. For example, a part of a small lot can be obtained at a lower cost, a part having a high precision can be obtained, and a part having a shape which is difficult to form by injection molding, can be easily prepared. Moreover, standard tools used for the machining of metals can be used for the machining of plastic stock.
Nevertheless, although conventional engineering plastics have excellent heat resistance, mechanical strength and the like, since machining stock is prepared by injection molding, the formation of a large part is difficult and the cost of a mold is high, and therefore, the molding process is limited. A so-called cast nylon product is a molded nylon article obtained by directly casting monomers in a mold and carrying out polymerization and molding in the mold, and according to this method, a larger product can be prepared, compared with injection molding or extrusion molding, but the product has a problem in that the water-absorbing property is high and the dimensional stability is poor.
Recently, technical developments have been made in the field of reactive injection molding (sometimes referred to as "RIM" hereinafter) using polycyclic norbornene monomers represented by dicyclopentadiene. A molded product obtained according to this method has a good heat resistance and water-absorbing property, but these molded products are generally thin and have a thickness smaller than 10 mm, and thick products such as machinable stock cannot be obtained. Furthermore, where a processing stock is prepared according to the RIM method, pores or voids having a size of 1 mm or more, or a size of 5 mm in an extreme case, which are called cavities, are often formed in the interior, and the stock is not suitable for machining.